Desiccant tablets for gas drying

ABSTRACT

Desiccant tablets including solid potassium formate are used to dry gas, especially in natural gas transmission lines. The most preferred tablets comprise 5-15% potassium formate, up to 1% of a surfactant as a lubricant, and the balance desiccant salts, preferably calcium chloride.

RELATED APPLICATION

[0001] This application is based upon and incorporates the entiredisclosure and claims of my Provisional Application Serial No.60/217,805 filed Jul. 12, 2000, and claims the full benefit of itsfiling date.

TECHNICAL FIELD

[0002] Tablets containing potassium formate are useful for drying gasesbecause of their deliquescent properties.

BACKGROUND OF THE INVENTION

[0003] In the past, desiccants have been commonly used to dry gases suchas natural gas, particularly for its transmission through pipelines.Typically the pipelines carry natural gas over hundreds of miles, and itis necessary and desirable to remove whatever moisture is present in thegas and/or in the pipeline. To this end, the art has employed commondesiccant salts such as calcium chloride, made into tablets which tendto absorb the moisture.

[0004] An early patent to Hutchinson, U.S. Pat. No. 2,804,940, suggestspassing a partially dehydrated natural gas upwards through a bed ofsolid particulate deliquescent material such as calcium, magnesium, orlithium chloride, or mixtures of them. Certain molar ratios of chloridesand bromides are suggested by Heath in U.S. Pat. No. 2,143,008 and byThomas in U.S. Pat. No. 5,733,841; see also Thomas U.S. Pat. No.5,766,309.for a good illustration of the placement of the soliddeliquescent materials in a contemporary drying vessel; this patent(5,766,309) is incorporated by reference herein in its entirety.

[0005] A solution of 40-70% potassium formate is suggested for use as amoisture absorbent in dehumidifiers and similar devices by Atkinson inU.S. Pat. No. 5,846,450.

SUMMARY OF THE INVENTION

[0006] Tablets are made of powdered or crystalline potassium formate andused to remove moisture from gases such as natural gas. The tablets maycontain from 0.5% to 100% by weight potassium formate, the balance beingalkali or alkaline earth metal formates (preferably sodium, calcium,cesium and/or magnesium formate), chlorides and/or bromides (preferablycalcium chloride, potassium chloride, cesium chloride, lithium chloride,or mixtures thereof). The tablet is preferably made under compressionand, for use in gas dryers in natural gas transmission lines, preferablyweighs about 7 to 15 grams so it can conveniently form a bed in a moreor less conventional gas dryer. A pillow shape is convenient, but noparticular shape is required for this invention. Preferred tabletscomprise 97.5% calcium chloride and 2.5% potassium formate. Anadditional 0.5% of a binder, which is preferably sodium laurylsulfonate, may also be used. The preferred tablets need not use theseexact proportions, however—they may comprise 0.5% to 100% potassiumformate, an additional 0.01% by weight to 1% by weight of a surfactantused as a lubricant, and the balance one or more alkali metal oralkaline earth metal halides.

DETAILED DESCRIPTION OF THE INVENTION

[0007] Comparisons have been made of the tablets of the presentinvention, containing potassium formate, to various tablets containingcalcium chloride. For the comparisons, tablets were made of each of thematerials indicated. Tablets of each description were placed in a screenbasket which in turn was placed in a humidifier and permitted to removemoisture from the same air. The baskets retained the tablets butpermitted liquid to drain into a pan. The pans were preweighed andweighed again periodically. Results are reported in terms of weight gain(liquid) in the pans, in grams, over time. Table I presents the dataobtained.

[0008] In Table 1 and elsewhere herein, CaCl2 77% is calcium chloridecontaining 23% moisture. 10% KCOOH means 77% CaCl₂ having an additional(based on the calcium chloride) 10% potassium formate. “94%+10% KF”means, in flake form, 94% calcium chloride, 6% moisture and anadditional 10% potassium formate based on the calcium chloride andmoisture. TABLE 1 Weight increase over time (grams) Product 3 hours 18hours 25 hours 90 hours CaCl2 77% 0.7295 4.609  6.5831 19.5703 CaCl2 77%0.4096 3.2685 4.5123 17.9454 +10% KCOOH 0.6026 6.0434 7.6411 19.6084+10% KCOOH 0.781  5.8817 7.7085 22.1131 94% + 10% KF 0.002  4.54835.6003 16.0585 94% + 10% KF 0.0931 3.2718 4.294  16.8932

[0009] TABLE 2 Weight increase over time (grams) Product 16 hours 20hours 24 hours 40 hours CaCl2 77% 8.9011 9.6635 10.0889  12.4836 94% +2.5% KF 6.9944 8.4999 9.5212 14.1517 94% + 5.0% KF 8.245  9.0611 9.631212.8922 94% + 7.5% KF 7.8536 8.7734 9.9184 13.9462 94% + 10% KF 7.259 8.1575 9.1607 13.2313

[0010] In Table 2, “94%+10% KF” means 94% calcium chloride, 6% moistureand an additional 10% potassium formate based on the calcium chlorideand moisture. “2.5% KF,” “5% KF,” and “7.5% KF” mean the indicatedpercentages of potassium formate in addition to the 94% calciumchloride. In Table 3, the term NH4F means ammonium formate. TABLE 3Weight Increase Over Time (grams) Hours Product 16 hrs 20 hrs 24 hrs 40hrs 77% CaCl2 6.547  8.5854 9.5619 15.3974 94% CaCl2 + 5% NH4F 4.964 6.3635 7.2397 12.9733 94% CaCl2 + 7.5% NH4F 8.2826 10.3386  11.3232 15.2833 94% CaCl2 + 10% NH4F 6.4756 8.0257 9.0649 13.1451

[0011] TABLE 4 Weight Increase Over Time 2 hours 5 hours 24 hours LiCi0.2913 1.8077 9.8172 KCOOH 0.5877 2.2647 9.993  77% CaCl2 0.0111 0.42464.9159 Sm. Mesh CaCl2 0.2023 0.5881 4.9159 Prilled CaCl2 0.0991 0.71364.6106

[0012] TABLE 5 Weight Increase Over Time 7 hrs 22 hrs 29 hrs 46 hrs 53hrs 70 hrs 77% CaCl2 2.7918 10.2764 12.082  15.7432 16.809  19.0542+2.5% 3.9704 11.7115 13.8077 17.9961 19.2392 21.8174 KCOOH +5.0% 3.863311.5287 14.0292 17.9577 19.0072 21.1038 KCOOH +7.5% 4.8065 10.766213.1887 16.4462 17.7821 19.7666 KCOOH +10.0% 4.7849 10.0518 12.782515.8435 17.2899 18.937 KCOOH

[0013] For Table 5, the indicated percentages of potassium formate wereadded to the standard 77% calcium chloride, which contained 23% byweight moisture at the beginning of the test. TABLE 6 Weight IncreaseOver Time 4 hrs 8 hrs 24 hrs 28 hrs 48 hrs 94% CaCl2 + 10% NaCl 0.81452.1562 8.3738  9.5873 15.6393 94% CaCl2 + 20% NaCl 1.4649 2.6146 8.4068 9.303  14.9175 100% KCOOH + 20% NaCl 2.0998 3.8347 10.8299  12.301115.5572 100% KCOOH + 20% NaCl 1.3877 2.6183 9.3758 11.2575 14.1278 94%CaCl2 + 20% CaBr₂ 0.8164 1.5235 6.7693  7.7308 13.4968

[0014] For Table 6, the indicated additions of sodium chloride andcalcium bromide were made to 94% calcium chloride in the case of thefirst, second and fifth tests, and to a 100% aqueous solution ofpotassium formate in the third and fourth tests.

[0015] In each case where potassium formate was present, the formationof the drained solution was faster than with compositions not includingpotassium formate. Potassium formate clearly absorbs more moisture, morereadily, than the other salts tested, and clearly enhances theseabilities for any of the solution combinations

[0016] Thus it will be seen that my invention comprises a deliquescentgas drying tablet comprising 0.5% to 100% solid potassium formate and 0%to 99.5% alkali, alkaline earth metal or ammonium formates, chlorides,bromides or mixtures thereof. The composition is preferably comprisesabout 5% to about 99.5% by weight potassium formate and most preferablyabout 5% to about 15% potassium formate with the balance being desiccantsalts such as alkali (including cesium), alkaline earth metal orammonium formates, chlorides, bromides or mixtures thereof, with calciumchloride being preferred.

1. A deliquescent gas drying tablet comprising 0.5% to 100% solidpotassium formate and 0% to 99.5% alkali, alkaline earth metal orammonium formates, chlorides, bromides or mixtures thereof.
 2. Adeliquescent tablet of claim 1 wherein the potassium formate comprisesabout 5% to about 99.5% by weight.
 3. A deliquescent tablet of claim 2comprising about 0.5% to about 95% calcium chloride.
 4. A deliquescenttablet of claim 1 wherein the potassium formate comprises 5% to 95% byweight of said tablet.
 5. A deliquescent tablet of claim 1 wherein thepotassium formate comprises 5% to 15% of said tablet.
 6. Method ofdrying gas comprising contacting gas with a bed of tablets comprisingpotassium formate thereby forming an aqueous solution of potassiumformate comprising water from said gas and potassium formate from saidtablet, and separating said solution from said bed of tablets.
 7. Methodof claim 6 wherein at least some of said solution is permitted to remainin contact with said bed of tablets and to contact said gas, wherebysaid solution continues to remove moisture from said gas until saidtablets are substantially dissolved.
 8. Method of claim 6 wherein saidtablets comprise 5% to 99.5% potassium formate.
 9. Method of claim 8wherein said tablets comprise about 5% to about 15% potassium formateand the balance is desiccant salts.
 10. Method of claim 6 wherein saidgas is natural gas.
 11. Method of claim 9 wherein said balance ofdesiccant salts comprise predominantly calcium chloride.
 12. Method ofclaim 6 wherein said separating is accomplished by draining.
 13. Methodof claim 7 followed by replacing said bed of tablets with new tabletscomprising solid potassium formate.
 14. Method of claim 13 followed byanother iteration of the method of claim
 13. 15. Method of claim 9wherein said desiccant salts include lithium chloride.
 16. Method ofclaim 9 wherein said desiccant salts include cesium chloride.
 17. Methodof claim 6 wherein contacting of said gas with said bed of tablets isaccomplished by flowing said gas upwardly through said bed of tablets.18. A desiccant tablet comprising about 5% to about 15% by weightpotassium formate, about 0.1 to 1% surfactant, and the balance at leastone desiccant salt.
 19. A desiccant tablet of claim 18 made bycompression, wherein said surfactant is sodium lauryl sulfonate.
 20. Adesiccant tablet of claim 18 wherein said at least one desiccant saltcomprises calcium chloride.